The field of the invention relates to electrical power drivers with fault monitoring provisions.
Electrical power drivers commonly employ a switching transistor coupled between a voltage source and a load such as an electronically actuated fuel injector. In response to an actuating signal, the switching transistor couples the voltage source to the load through its dynamic impedance. Various attempts have been made to incorporate diagnostics with the power driver. For example, U.S. Pat. No. 4,589,401 issued to Karim et al discloses a power driver having diagnostic capability. Current sensing through the load is coupled to a microcomputer for inferring either short circuit or open circuit fault conditions. More specifically, when current is detected during the absence of an actuating signal, the microcomputer infers a short circuit condition. Similarly, when current is not sensed during an actuating signal, the microcomputer infers an open circuit condition.
Another example of a power driver having some form of fault diagnosis is provided by a Siemens device designated as SMT 12 SMART-SIPMOS.TM.. Sensing circuitry is coupled to a FET transistor for providing indications of open circuit, short circuit, over temperature, and under voltage conditions. These fault indications are provided on a status output pin by toggling the input and monitoring changes in status output. Additional external circuitry is required to infer the fault type from the input changes and the corresponding changes in status output.
The inventors herein have recognized numerous disadvantages with the fault detection approaches described above. For example, the inventors herein contend that these prior approaches do not provide a servicing technician with indications of whether a particular fault is new, or old, or intermittent. Further, the inventors herein contend that relatively sophisticated external microcomputer programming is required to infer a particular fault type from the prior devices. These disadvantages are particularly severe in a modern automobile environment having numerous electronically actuated devices and complex electrical interconnections or cabling. Accordingly, service technicians commonly replace allegedly defective components which are actually not defective. Further, technicians are often unable to repair intermittent failures.